G7 leaders tell Russia to halt Crimea referendum

Pro-Russian supporters shout slogans during the rally in Sevastopol bay on March 12, 2014. (AFP)

Leaders of the Group of Seven economies told Russia to stop its work on a referendum in Ukraine's Crimea region and "cease all efforts to change the status of Crimea" or face action.

"In addition to its impact on the unity, sovereignty and territorial integrity of Ukraine, the annexation of Crimea could have grave implications for the legal order that protects the unity and sovereignty of all states," the G7 leaders said in a statement released by the White House.

"Should the Russian Federation take such a step, we will take further action, individually and collectively," they said.